Richard Seager, a senior research scientist with the Lamont Doherty Earth Observatory, and co-authors report their findings today in the online advance version of the journal Science.

Based on the climate models, the U.S. Southwest and parts of northern Mexico could become as arid as the North American Dust Bowl conditions of the 1930s, the study authors report.

"If these models are correct, the levels of aridity of the recent multiyear drought [will] become the new climatology of the American Southwest," the team writes.

Persistent Drought

In general the computer models all predict decreasing precipitation in the subtropics in both hemispheres.

The long-term drying of southwestern North America is part of that pattern. Changes in atmospheric circulation and water-vapor transport are expected to alter the region's climate as the planet warms.

Seager said the most surprising finding is that "this drying trend in the subtropics becomes so clear very early in the current century."

In fact, long-term drying may have already begun, the authors say.

Persistent La Niña-induced temperature fluctuations in the Pacific Ocean caused a drought between 1998 and 2002 that was much like earlier droughts during the 1930s and '50s.

La Niña, the cold-water cousin of El Niño, is a phenomenon in which the Equatorial Pacific experiences unusually cold sea-surface temperatures. The event is associated with drier winters in the U.S. Southwest.